Two-stroke internal-combustion engine



June 21, 1938. H. R. RICARDO 2,121,409

TWO-STROKE INTERNAL COMBUSTION ENGINE Filed Oct. 15. 1935 2 Sheets-Sheet 1 Fig. 1.

INVENTOR June 21, 1938. H. R. RICARDO 2,121,409

TWO-STROKE INTERNAL COMBUSTION ENGINE Filed Oct. 15, 1935 2 Sheets-Sheet 2 D Fig. 3. D

c E I C IVVFA T R mms.

Patented June. 21, 1938 UNlT ED STATES 'rwo-s'raoxr. INTERNAL-COMBUSTION ENGINE a Harry Ralph Ricardo, London, England Application October 15, 1935, Serial No.

In Great Britain October 19, 1934 6 Claims.

This invention relates to two-stroke internal combustion engines of the kind wherein a single sleeve valve which may have a combined oscillating and reciprocating motion controls the discharge of exhaust gases through one or more exhaust ports or openings in the cylinder wall adjacent to the cylinder head sion of scavenging air takes place through one or more ports or openings in the wall of the sleeve valve towards the end 01' the working chamber remote from the head.

For the sake of convenience the end oi! the cylinder, sleeve and other parts adjacent to the cylinder head will be referred to as the upper end.

In a two-stroke internal combustion engine or the kind referred to-according to the present inbetween the vention the exhaust adjacent to the head of the end 01' are formed in ports .in the cylinder wall are controlled by the edge the sleeve valve so that no ports this end portion of the sleeve. No gas-tight part carried by the cylinder head extends into and engages the adjacent end of the bore of the sleeve and the sleeve reciprocates only piston and the cylinder wall. The end part or the sleeve which controls or determines the uncovering of the exhaust ports is conveniently made thinner than the remaining or main portion of the sleeve or is otherwise. weakened so that this part of the sleeve can expand under the internal gas pressures during operation of the engine to assist in maintaining a substantially fluid-tight joint between this part of the sleeve which lies above the exhaust ports during the compression and firing periods and the cylinder wall. Further, the arrangement is conveniently such that the part of the sleeve which covers the exhaust ports during the later part of the compression stroke and the earlier part of the firing stroke of the piston is then shielded by the piston from internal gas pressure, the arrangement preferably being such that at the end of the piston stroke the uppermost piston ring lies with its upper edge in or beyond the plane of the upper edge of the exhaust ports; In this way,

while expansion of the wall of the upper end portion of the sleeve under internal gas pressure can take place to assist in maintaining a substantially gas-tight joint between this part of the sleeve and the cylinder wall, the risk of distortion of the wall of the sleeve due to the internal gas pressure tending to cause this wall to be forced into the exhaust ports around it nated.

Where, as described above, the sleeve is made thinner over that end portion which lies above is reduced or elimiwhile the admisthe exhaust ports during the high pressure part of the cycle than the remaining part of the sleeve, the thinned part may either be of substantially constant thickness or tapered, while the remaining part of the sleeve may either be of uniform 5 thickness throughout its length or may be thickened over that part in which the inlet or scavengihg ports are formed. This latter arrangement is convenient, for example, where the thickening constitutes a strengthening band at the part to which the mechanism for imparting movement to the sleeve is attached. In any case, the scavenging ports may be so formed that the charge entering through them has imparted to it a substantial component in a tangential direction within the cylinder. The obliquity of the inlet ports for this purpose is determined in accordance with the degree of swirl which it is desired to impart to the incoming charge as may be requisite according to whether the invention is applied to an engineof the compression ignition type in which this swirl is utilized to assist the distribution of fuel throughout the air or to an engine operating with spark ignition in which less swirl is usually preferable or, again, to engines of the compression ignition type wherein little or no swirl about the cylinder axis is required, any organized turbulence or the air charge which may be required being efi'ected in some other way, for example by forcing the air'charge during the compression stroke from the cylinder bore into a combustion chamber through one or more restricted passages. The arrangement is preferably such that at maximum opening of the exhaust ports the upper edge of the sleeve does not lie above and is preferably substantially coincident with the lower edge of the exhaust ports.

The invention may be carried into practice in various ways, but one construction according to this invention as applied to an engine operating 40 on the liquid fuel injection compression ignition system and two modifications thereof are illustrated somewhat diagrammatically by way of example in the accompanying drawings, in which Figure 1 is a sectional elevation,

Figure 2 is a section in the plane 2-2 of Figure 1,

Figure 3 is a sectional elevation of part of the upper end of the cylinder and of the cylinder head showing one modification, and 5 Figure 4 is a sectional elevation showing a modcation which may be made to the upper end of the sleeve valve. i

In the construction illustrated in Figures 1 and 2 the engine, comprises a crank case A having 55 of an aluminium alloy.

2 mounted therein a crankshaft B and connected to a water-cooled cylinder C which may be formed To the upper end of the cylinder C is secured a cylinder head D contain-l ing a water-cooled combustion chamber D of smaller diameter than the cylinder bore provided with a fuel sprayer D, the axis of which lies substantially parallel to the axis-of the cylinder and combustion chamber and is displaced from the combustion chamber axis. Formed in the wail of the cylinder C adjacent to its upper end are a series of exhaust ports C communicating with exhaust galleries C' provided with outlets at C adapted to be attached to an exhaust pipe. Also formed in the cylinder at a point adjacent to the upper end of the crank case is a circumierentially arranged inlet or scavenging gallery 0 to which scavenging air under pressure is supplied, for example in known manner from a blower.

Mounted within the cylinder is a sleeve valve E formed, for example, of steel in the wall of which is formed a series of inlet or scavenging ports 1: communicating withthe inlet gallery and arranged tangentially with respect to a circle having for centre the axis of the cylinder so that the scavenging air passing therethrough from the inlet gallery C will tend to rotate about the cylinder axis.

The sleeve E is provided at its lower end with a thickened part E rigidly connected to or formed integral with which is a pin E freely engaging a bore in a member F the outer surface of which is part-spherical and is freely mounted in a correspondingly internally part-spherical member F mounted on the upper end of a coupling rod F an intermediate point in which is pivoted to one end of a link I", the other end of which is pivoted to the crank case A, while the lower end of 44Tthe rod 1 is provided with a strap F engaging an eccentric F secured to the crankshaft B. This mechanism will impart a combined oscillating and reciprocating motion to the sleeve in known manner.

A piston G reciprocates within the sleeve valve E and is connected by a connecting rod G to a crank B on the crankshaft B in known manner.

The crank B and the eccentric F are approximately in phase so that while a combined oscillating and reciprocating motion will be imparted to the sleeve E in known manner, the end of the upward movement of the sleeve will nearly coincide with the end of the upward or compression stroke of the piston, while the end of the downward movement of the sleeve will coincide with the end of the downward or firing stroke of the piston, the upper edge of the sleeve at the end of its downward movement preferably substantially coinciding with the lower edge of the exhaustports.

The bore of the upper end portion of the sleeve E, which at the of the sleeve lies above the exhaust ports, is tapered or reduced in thickness as shown at E while the upper end of the cylinder bore may be tapered to a small degree which cannot be readily illustrated, the smaller diameter of the taper in the cylinder bore being adjacentto the upper end of the cylinder, and the taper extending downwards to a point adjacent to the upper edge of the exhaust ports 0 This taper is such that the bore of the upper end of the cylinder has a diameter which, in a cylinder having a bore of the order of flve and a half inches diameter, is of the order of two thousandths of an inch end of the upward movement less'than the bore of the cylinder below the exhaust ports. The provision of this taper, while being in some cases desirable where an aluminum alloy or like high expansion cylinder is employed, would in general be unnecessary where a cast iron cylinder were used.

The thickness of the main part of the wall of the sleevevalve E and of the upper part of reduced diameter may vary, but in an engine of the compression ignition type such as that shown, having a sleeve the internal diameter of which is of the order of flve and a half inches, the thickness of the part of the sleeve which at the end of its upstroke lies above the exhaust ports,

is preferably of the order of one per cent or less of the sleeve diameter where the sleeve is formed of steel, this thickness being such that this upper end part of the sleeve will expand under the internal pressure towards the end of the compression stroke and during the firing period to assist in maintaining a fluid-tight joint between it and the cylinder wall.

A circumferential oil groove 0 is formed in the cylinder wall at a point between the scavenging gallery C and the exhaust ports C oil being fed under pressure to this groove through a The operation of the engine is as follows:

As the piston G moves downwards from its upper dead centre on the firing stroke, the sleeve E also moves downwards but more slowly, and the upper edge of the sleeve begins to uncover the exhaust ports C just before the piston G begins to uncover the scavenging ports E in the sleeve valve. The exhaust period thus begins shortly before the admission of scavenging air through the scavenging ports, so that the waste gases are driven out and the working chamber is charged with air in readiness for the next compression stroke, this air being in a state of rotation about the cylinder axis due to the tangential arrangement of the scavenging ports E. the later part of the compression stroke of the piston and the early part of the firing stroke it will be seen that the part of the wall of the sleeve E then covering the exhaust ports C is shielded by the piston G from internal gas pressure. Thus, though the pressure within the working chamber can then act upon the wall of the sleeve valve lying above the exhaust ports, thereby expanding this part of the sleeve to assist in maintaining gas-tight engagement thereof with the adjacent part of the cylinder wall, the internal pressure, when at or near its maximum value, cannot act on that part of the sleeve lying immediately over the exhaust ports C The tendency for the wall of the sleeve valve E to be expanded into the exhaust ports C by the internal gas pressure is thereby reduced.

It will be seen that the exhaust ports are controlled not by ports in the sleeve valve but by the adjacent edge of the sleeve valve and that the tendency for the thin portion of the sleeve to expand under the internal gas pressure during the compression and firing strokes tends to maintain a gas-tight fit between the upper end portion of the sleeve and the cylinder, this gas-tight fit between the upper end of the sleeve valve and the adjacent part of the cylinder being greatest when the pressure is highest. The necessity for providing a plug-like cylinder head which projects into the cylinder, as has hitherto been common practice, with head rings between the sleeve and the plug-like head, is thus obviated and the coolor at least the upper edge portion of such part,-

Durin ing of the combustion chamber is also facilitated since this chamber does not have to be formed within the plug-like cylinder head and can therefore be directly accessible. Furthermore, the absence of head rings as are used on plug-like cylinder heads ensures that 'difllculties due to carboning-up of the head rings, which difliculty is more liable to occur in engines of the two-stroke than in these of the four-stroke type, cannot arise.

It will be appreciated that since there are no ports in the part of the sleeve valve E adjacent to the exhaust ports, this part can be made sufficiently thin to permit the desired expansion under theaction of internal gas pressure, while any possibility of warping occurring due to the bars or bridges which would be necessary between adjacent ports if such were provided in the thin part of the sleeve valve. due to heat flow, is avoided.

The lubrication of the lower part of the sleeve may be effected in some known manner by splash from the crank case, while the upper part of the sleeve is lubricated by oil from the oil groove C 1 this 011 being carried to the extreme upper part of the sleeve across the bars which divide the exhaust ports (2 in the cylinder, the combined oscillating and reciprocating movement of the sleeve tending generally to distribute oil and maintain adequate lubrication over the whole of the outer surface of the sleeve.

The bars 0 are conveniently of somewhat streamline form on their sides remote from the cylinder bore for tendency for carbon to form thereon.

Figure 3 shows a modified arrangement which in some cases may be desirable, and may be applied to an engine otherwise similar to that shown in Figures 1 and 2, wherein the upper end portion of the cylinder barrel is constituted by a separate member or liner H having a flange H lying between the upper end of the cylinder proper and the cylinder head D. This liner may be particularly convenient where an aluminium cylinder is employed, the sleeve being of normal steel, and not only provides the working surface for the upper end portion of the sleeve which serves to seal the exhaust ports, but also provides a member which can readily be replaced in the case of wear taking place. In such a case the liner H is preferably of cast-iron or other material having about the same expansion coefiicient as the sleeve.

Fig. 4 shows a modification of the upper end of'the sleeve which may also be applied to an engine similar in other respects to that shown in Figures 1 and 2, wherein the upper end portion of the sleeve is formed separately from the main part of the sleeve and is constituted by an annular part E connected to the main part E of the sleeve by a circlip E engaging a shoulder on the part E and a groove in the part E as shown, the engaging surfaces of the parts E and E being somewhat cut away, as shown at E to ensure that there shall be a gas seal between the inner edges of these parts and that pressure within the cylinder will thus tend always to maintain the part E in close contact with the part E.

The parts E and E in this construction may be formed of different metals or may be formed of the same metal, the arrangement in either case permitting the part E to be renewed in the case of wear thereof taking place. In particular, where the cylinder is of aluminium alloy or other high-expansion material, and the sleeve of carhon-steel or other low-expansion material, the

-the purpose of reducing the part-E may be of a high-expansion material such as an austenitic steel or cast-iron.

It is to be understood that the construction more particularly described above is given by way-of example and that details may be modified without departing from this invention. For example, the invention may be applied to an engine in which the cylinder and cylinder head are aircooled and to engines of the vaporized charge spark ignition type, while the mechanism for operating the sleeve and other details of construction may be modified considerably.

Further, the invention may be applied to double-acting two-stroke engines, in which case the sleeve would be operated from a point intermediate in its length and each end thereof would be formed and arranged to cooperate with exhaust ports in the manner according to this in vention, scavenging ports, of which a single set may be common to both working chambers, being provided at a point intermediate in the length of the sleeve.

It is also to be understood that, although in the present specification and the followi ng claims exhaust ports are referred to, this expression is to be interpreted as including a single continuous exhaust slot undivided by bars engaging the outer surface of the sleeve.

I claim:-

1. An internal-combustion engine, comprising a cylinder with a cylinder head and provided in its wall with exhaust ports adjacent to said head, the part of the cylinder bore on the side of the exhaust ports nearest to the cylinder head being provided with a slight taper, the smallest diameter of which is adjacent to the cylinder head; a piston operable in said cylinder; and a sleeve valve movable between the piston and the cylinder and controlling the exhaust ports with the edge at one end of the sleeve.

2. A two-stroke internal combustion engine according to claim 1, in which the taper of the cylinder bore is such that the end of the cylinder bore adjacent to the cylinder head has a diameter which is of the order of of the diameter of the cylinder bore less than the diameter of the part of this bore at that side of the exhaust ports which is remote from the cylinder head.

3. A two-stroke internal combustion engine comprising a cylinder with a cylinder head and provided in its wall with exhaust ports adjacent to the said head, a piston operable in said cylinder and a sleeve valve movable between the piston and the cylinder wall and controlling the exhaust ports of the cylinder wall by its edge, the end portion of the sleeve which at the end of its stroke towards the cylinder head lies beyond the exhaust ports being weakened as compared with the remaining portion of the sleeve, the thickness of said part of the sleeve being at its edge of the order of not more than one per cent of the diameter of the cylinder bore.

4. A two-stroke internal combustion engine, comprising a cylinder with a cylinder head and provided in its wall with exhaust ports adjacent to said head and a scavenging air belt remote from the exhaust ports, the part of the cylinder boreon the side of the exhaust ports nearest to the cylinder head being provided with a slight taper, the smallest diameter of which is adjacent to the cylinder head; a piston operable in said cylinder; and a sleeve valve movable between the piston and the cylinder and controlling the exhaust ports.

'5. A two-stroke internal combustion engine,

comprising a cylinder provided to said head and scavenging air belt remote from the exhaust ports, the part oi the cylinder bore on the side of the exhaust portsnearest to the cylinder head being provided with a-slight taper, the smallest diameter of which is adjacent to the cylinder head; a piston operable in said cylinder; and a sleeve valve movable between the piston and the cylinder and controlling the exhaust ports, at the end of its stroke towards the cylinder head lies beyond the exhaust ports being weakened as compared with .the remaining portion or the with a cylinder head and in its wall with exhaustports adjacentthe end portion oi the sleeve which sleeve to such extent that it can expand'under internal gas pressure during operation of the en glue and thus tend to maintain a substantially fluid-tight Joint between it and the cylinder wall.

6. A two-stroke internal combustion engine according to claim-4. in which the taper oi the cylinder bore is such that the end 0! the cylinder bore adjacent to the cylinder head has a diameter which is of the order of 00 0! the diameter of the cylinder bore less than the'dimeter of the part of this here at that side or the exhaust ports which is remote from the cylinder head.

HARRY RALPH RICARDO. 

